From Chapter i. of “De Jure Belli et Pacis.”

NATURAL Law is the Dictate of Right Reason, indicating that any act, from its agreement or disagreement with the rational (and social) nature (of man) has in it a moral turpitude or a moral necessity; and, consequently, that such act is forbidden or commanded by God, the author of nature.

  Acts concerning which there is such a Dictate are obligatory (morally necessary), or are unlawful in themselves, and are therefore understood as necessarily commanded or forbidden by God; and in this character Natural Law differs, not only from Human Law, but from Positive Divine Law, which does not forbid or command acts which, in themselves and by their own nature, are either obligatory or unlawful; but by forbidding them makes them unlawful, by commanding them make them obligatory.

  In order to understand Natural Law, we must remark that some things are said to be according to Natural Law, which are not so properly, but, as the schools love to speak, reductively, Natural Law not opposing them; as we have said that some things are called just, which are not unjust. And again, by an abuse of expression, some things are said to be according to Natural Law which reason shows to be decent, or better than their opposites, though obligatory. (As monogamy is better, though we cannot strictly say that polygamy is contrary to Natural Law.)

  It is to be remarked also that Natural Law deals not only with things made by Nature herself, but with things produced by the act of man. Thus property, as it now exists, is the result of human will; but being once introduced, Natural Law itself shows that it is unlawful for me to take what is yours against your will. And thus Paulus says that theft is prohibited naturali jure; Ulpian says that it is natura turpe, bad by nature; Euripides says it is displeasing to God.

  Natural Law is so immutable that it cannot be changed by God himself. For though the power of God be immense, there are some things to which it does not extend: because if we speak of those things being done, the words are mere words, and have no meaning, being self-contradictory. Thus God himself cannot make twice two not be four; and, in like manner, he cannot make that which is intrinsically bad, not be bad. For as the essence of things, when they exist, and by which they exist, does not depend on anything else, so is it with the properties which follow that essence: and such a property is the baseness of certain actions, when compared with the nature of rational beings. And God himself allows himself to be judged of by this rule.

  Yet sometimes, in acts directed by Natural Law, there is a seeming of change, which may mislead the unwary; when in fact it is not Natural Law which is changed, but the thing about which that Law is concerned. Thus, if a creditor give me a receipt for my debt, I am no longer bound to pay him; not that Natural Law has ceased to command me to pay what I owe, but because I have ceased to owe it. So if God command any one to be slain or his goods to be taken, this does not make lawful homicide or theft, which words involve crime: but the act will no longer be homicide or theft, being authorized by the supreme Lord of life and of goods. Further, some things are according to Natural Law, not simply, but in a certain state of things. Thus a community in the use of things was natural till property was established; and the right of getting possession of one’s own by force existed before instituted law.

  What the Roman law books say of a law of nature which we have in common with animals, which they call more peculiarly jus naturæ, besides the natural law which we have in common with men, which they often call jus gentium, is of little or no use. For no creature is properly capable of Jus, which does not by nature use general precepts: as has been remarked by Hesiod, Cicero, Lactantius, Polybius.

  If we ever assign justice to brute animals, it is improperly, when we see in them some shadow or vestige of reason. There are acts which we have in common with brutes, as the rearing of offspring; and others which are peculiar to us, as the worship of God, but this has no bearing on the nature of Jus.

  That there is such a thing as Natural Law is commonly proved both a priori and a posteriori; the former of the more subtle, the latter the more popular proof. It is proved a priori by showing the agreement or disagreement of anything with the rational and social nature of man. It is proved a posteriori when by certain or very probable accounts we find anything accepted as Natural Law among all nations, or at least the more civilized. For a universal effect requires a universal cause: now such a universal belief can hardly have any cause except the common sense of mankind.

  Hesiod, Heraclitus, Aristotle, Cicero, Seneca, Quintilian, agree that the consent of all nations is evidence of the truth. And Porphyry, Andronicus of Rhodes, Plutarch, Aristotle, agree that the more savage nations are of less weight in such an estimate.

  Thus much of Natural Law; next of Positive or Instituted Law. And this is either Human or Divine.

  Of Human Law, first, as more widely known.

  This is either the Civil Law (that is, the National Law), or Law in a narrower, or in a wider sphere.

  The Civil Law is that which governs the State.

  The State (Civitas) is a perfect (that is, independent) collection of free men, associated for the sake of enjoying the advantages of jus, and for common utility.

  Law in a narrow sphere, and not derived from the State, though subject to it, is various, as paternal precepts, the commands of a master, and the like.

  Law in a wider sphere is Jus Gentium, the Law of Nations, that Law, which has received an obligatory force from the will of all nations, or of many.

  I have added “or of many,” because scarce any Law is found, except Natural Law (which also is called Jus Gentium), common to all nations. Indeed, that is often Jus Gentium in one part of the world which is not so in another; as we shall show when we come to speak of captivity and of postliminium.

  This Jus Gentium, Law of Nations, is proved in the same manner as the unwritten Civil Law, by constant usage, and the testimony of those who have made it their study. It is, as Dio Chrysostom says, the invention of life and time. And here the best historians are a great help to us.

  What is Divine (instituted) Law is sufficiently apparent from the term itself; namely, that which has its origin from the Divine Will; by which character it is distinguished from Natural Law, which also may be called Divine (but which is independent). In such Law it may be said, but with reserve, that God did not command the act because it was just, but that it was just because God commanded it.

  This Law is given either to the whole human race, or to one nation. To the human race, the Law has thrice been given by God: at the Creation, immediately after the Deluge, and at the coming of Christ. These three sets of Laws oblige all men, as soon as they acquire a sufficient knowledge of them.